Respiration requires organic molecules like glucose as fuel. Glucose is broken down through a series of steps to release chemical energy. In glycolysis, glucose is split into two pyruvate molecules in the cytoplasm. This produces two ATP molecules and reduces two NAD molecules. If oxygen is present, pyruvate enters the mitochondrion where it is converted to acetyl CoA and enters the Krebs cycle to further oxidize molecules, reducing NAD and FAD. These reduced carriers transfer hydrogen to the electron transport chain, generating ATP. Oxygen is the final hydrogen acceptor.

1. Respiration
overview

2. Respiration requires organic
molecules to be used as fuel
The starting molecule is usually
glucose
It is broken down in a series of
steps
This will give potential chemical
energy

3. In the first step glucose
is split
This stage is called
glycolysis
In a series of enzyme
controlled reactions two
molecules of pyruvate
are made

4. Pyruvate can stay in the
cytoplasm and enter into
the anaerobic pathway
This occurs in the
absence of oxygen

5. If oxygen is present
pyruvate enters the
mitochondrion
It is converted to Acetyl
CoA in the Link reaction

6. This molecule now
enters the Krebs
Cycle where NAD and
FAD are reduced
Most of the CO2 is
made at this stage

7. The reduced molecules
carry Hydrogen to the
Electron transfer Chain
This generates ATP
The final hydrogen
acceptor is oxygen

8. Hydrogen Carrier Molecules
There are two of these in respiration
NAD
Nicotinamide Adenine Dinucleotide
This is a co-enzyme
This can accept electrons and hydrogen and
become reduced
FAD
Flavin adenine dinucleotide
It is derived from Vitamin B2 (riboflavin)

9. NAD NADreduced
NAD is a hydrogen carrier molecule
When it picks up hydrogen it becomes
reduced

10. FAD is more complex – all you need to know
is it will carry hydrogen to the final stage of
respiration

11. Glycolysis

12. This is the splitting of sugar or more
specifically glucose
It takes place in the cytoplasm
6 Carbon glucose is split into 3 Carbon
Pyruvate in a series of steps
ATP is used in the first steps but
generated in the last few steps
NAD is reduced

13. In the first steps of glycolysis glucose
has 2 phosphates attached
We say glucose is phosphorylated
These are transferred from ATP
So two ATP molecules are used
A hexose biphosphate is made
We will tally the
NAD reduced
made here
We will keep tally
of ATP here

14. This hexose phosphate is split into TWO triose
(3C) phosphates
So from her onwards everything must
be X2 for each molecule of glucose

15. The 3 Carbon phosphates
look like this in case you
are interested

16. Each triose phosphate then have a hydrogen removed
This is attached to NAD which becomes NADreduced
This is an energy yielding step – ADP is phosphorylated
to ATP

17. Another phosphate is lost to form Pyruvate and another ATP

18. Pyruvate looks like
this
It is an acid

21. So the products of
glycolysis of one molecule
of glucose are:
2 x pyruvate
2 x NADreduced
2 x ATP (net)